Members of a cross collaboratory team from the MIT Lincoln Lab and the main campus at MIT, including EECS Professor Terry Orlando and Karl Berggren, the Emanuel E. Landsman Career Development Associate Professor in EECS, have reported on a new technique for characterizing artificial atoms (or quantum entities) over very broad frequency ranges, a necessary step in the quest for super-fast quantum computing. The work is featured in the Sept. 4 issue of Nature.

As reported from the MIT Lincoln Laboratory and by the MIT News Office in their Sept. 3 article, ever since Nobel Prize-winning physicist Richard Feynman first proposed the theory of quantum computing over two decades ago, researchers have been working towards making this kind of device possible.

William Oliver member of the Lincoln Lab's Analog Device Technology Group and the MIT Research Lab of Electronics, RLE, described the difficulties that are posed when using an earlier technique with superconducting devices. On cooling to nearly absolute zero (-459 degrees F, -273 degrees C), these entities will behave like artificial atoms or nanometer-scale "boxes" in which electrons are forced to exist at specific, discrete energy levels. Unfortunately, Oliver explained, traditional scientific techniques for characterizing and understanding atoms and molecules--such as spectroscopy--do not work for the wide frequencies, ranging from tens to hundreds of gigahertz typical of these artificial atoms.

The beauty of the new procedure--amplitude spectroscsopy--developed by the Lincoln Lab/MIT team, is that it enables characterization of quantum entities over extremely broad frequency ranges, making it ideal for studying the properties of artificial atoms. Amplitude spectroscopy measures the response of a superconducting artificial atom by probing its response to a single, fixed frequency--pegged at a state chosen as 'begnign.' Once pushed by the probe through its energy-state transitions, the atoms are made to jump between energy bands at practically unlimited rates by adjusting the amplitude of the fixed-frequency source.

Emitted radiation by the articicial atoms in response to this probe exhibits interference patterns, called "spectroscopy diamonds." Because of their unique geometric regularity, 'fingerprints' can be determined for each artifical atom's energy spectrum.

This new tool which will lead to better knowledge of superconducting structures and ultimately the development of a quantum computer, was funded by the Air Force Office of Scientific Research, the Laboratory for Physical Sciences, the Department of Defense and the US government.